1. Field of the Invention
The present invention relates to a substrate processing apparatus and a substrate processing method that heats and/or cools a substrate, and a computer-readable storage medium storing a program for causing the substrate processing apparatus to perform the substrate processing method.
2. Description of the Related Art
A coater/developer for coating an organic material film such as a resist film or the like on a substrate and developing the film is provided with a substrate processing apparatus for heating and/or cooling the substrate.
As an example of such a substrate processing apparatus, a substrate heating apparatus 101 is described in reference to FIG. 1. In the substrate heating apparatus 101, a substrate 103 is placed on a thermal plate 102 and heated by a heater 104 embedded in the thermal plate 102. During heating the substrate 103, nitrogen is supplied toward the substrate 103 so as to purge volatile substances such as organic solvents from the organic film. While the nitrogen or the like is exhausted by an exhaust apparatus 110, the volatile substances are collected by a collection portion 105. In such a substrate heating apparatus 101, when the back surface of the substrate 103 directly contacts the top surface of the heating plate 102, particles may be attached on the back surface of the substrate 103. In order to avoid the particles attaching on the back surface, the thermal plate 102 is provided with plural pins 108 and the substrate 103 is placed on the plural pins 108. In this configuration, the substrate 103 is heated through an air layer, which is generally referred to as a proximity gap, formed between the back surface of the substrate 103 and the top surface of the thermal plate 102.
By the way, when a film, for example, a resist film is formed on the substrate 103, the stress between the film and the substrate 103 may cause the substrate 103 to be warped into a bowl (or concave) shape or a dome (or convex) shape. In order to uniformly heat the substrate 103 even in this situation, there is known a thermal processing technique in which the heat plate 102 is provided with plural suction conduits 106 through which the substrate 103 is attracted onto the heat plate 102 by a vacuum pump 107, thereby maintaining the substrate 103 to be flat with respect to the heat plate 102.
The technique is described in reference to FIGS. 2A through 2B, where the concavely warped substrate 103 is used. As shown in FIG. 2A, when the substrate 103 is placed on the heat plate 102 and if the suction through the suction conduits 106 is not in operation, the substrate 103 is concavely warped. In this case, a lowest portion of the substrate 103 (or a center bottom portion of the bowl-shaped substrate 103) sits on the pins 108 and circumferential portions of the substrate 103 are separated from the pins 108. When the substrate 103 is suctioned through the suction conduits 106, a portion of the substrate 103 that is closer to the heat plate 102 (or a portion around the center bottom portion) is strongly drawn to the heat plate 102 and comes in contact with the pins 108 as shown in FIG. 2B. In this manner, the substrate 103 is straightened so as to be flat with respect to the heat plate 102.
By the way, the heat plate 102 may be situated in a down-flow environment of nitrogen or the like. In this case, the nitrogen flows inward from the circumference to the center of the substrate and thus into the suction conduits 106. Therefore, a large amount of nitrogen has to be evacuated in order to attract the substrate 103 onto the heat plate 102 (the pins 108). However, if the suction performance of, for example, the vacuum pump 107 is strengthened, an excessively large force may be locally applied to the substrate 103, resulting in damage to or breakage of the substrate 103 in some circumstances, as shown in FIG. 2C. Or, even if the substrate 103 is not damaged or broken, more time is required to attract the substrate 103, if the substrate 103 is severely warped. When it takes more time, the heat plate 102 is cooled for a longer time by the nitrogen flow, which may require more thermal energy to be supplied to the heat plate 102. In addition, when more time is needed to straighten the substrate 103, the temperature uniformity of the heat plate 102 may become worse because the heat plate 102 can be cooled unevenly by the nitrogen, which impairs the thermal process that should uniformly heat the substrate 103.
In addition, while volatile substances or the like, which may be caused by heating the substrate 103 and the film on the substrate 103, are mainly evacuated along with the nitrogen, for example, by an evacuation apparatus 110 and collected by a collecting portion 105, part of the substances may be evacuated through the suction conduits 106. The volatile substances flowing through the suction conduits 106 may be cooled to be condensed on the inside wall of the suction conduits 106, thereby narrowing the inner diameter of the suction conduits 106. As a result, the suction performance is impaired, so that the substrate 103 may no longer be attracted.
Patent Document 1 listed below discloses a technique in which a degree of substrate warpage is measured in advance and the suction performance or an amount of gas blown onto the substrate is adjusted between in the inner area and in the outer area of the heat plate in accordance with the measurement result so as to hold the substrate flat with respect to the heat plate. However, this technique cannot completely eliminate the above disadvantages because a large amount of gas may need to be suctioned from the suction conduits at the outer area, which may lead to damage in the substrate, although this technique is advantageous compared with a heat plate where the substrate is attracted entirely at the same suction performance.
In addition, Patent Document 2 discloses another technique that can reduce temperature variations throughout the substrate by substantially confining the air layer between the substrate and the heat plate so as to prevent air from flowing therebetween. While this technique may properly keep the substrate flat, it cannot be employed when the edge area of a back surface of the substrate is contaminated by a resist solution, since the contaminated edge area contacts a top surface of the heat plate so as to produce particles from the resist.
Patent Document 1: Japanese Patent Laid-Open Publication No. 2006-210400 (paragraph 0042 and 0045, FIGS. 6 and 7).
Patent Document 2: Japanese Patent Laid-Open Publication No. H06-338450 (paragraph 0027).
The present invention has been made in view of the above, and is directed to a substrate processing apparatus and method that can hold the substrate flat with respect to a heat exchanging plate of the substrate processing apparatus by suction and prevent an excessively large force being applied to the substrate.